Optical sheets, such as light diffusion sheets, prism sheets, polarizing sheets or the like, are used in backlit type liquid crystal display devices for large-scale liquid crystal television apparatus and the like. However, until the present time, for fixing and retaining these types of optical sheets on a chassis of the display device, individualized fixing structures have been designed and manufactured respectively for each type of display device. Further, operations for fixing and retaining such optical sheets, as well as for removing the optical sheets for carrying out repairs and the like, have involved different complex operations for each type of machine.
As one fixing structure for optical sheets, as disclosed in the following Patent Document 1, a surface light source device is known. Patent Document 1 discloses that a frame is assembled integrally around the periphery of a light transmission plate having fluorescent lamps mounted on both side surfaces thereof. A prism sheet, a diffusion sheet, and a reflective sheet are prepared in a stacked condition, corresponding to front and rear parts of the light transmission plate, and fixing and retention thereof is carried out by engaging projections on the side of the light transmission plate, and engaging recesses on the side of the frame.
Further, the chassis of a large scale flat display device such as a large-scale liquid crystal television apparatus or the like previously has been manufactured by a sheet metal punching process or a press formation process. However, when a large-scale screen chassis is used, a large sized sheet metal material must be used as well, and a core that is made by punching the central region of the sheet metal material is also rendered large in size in proportion thereto. The core is treated as unnecessary scrap material, which is created upon manufacturing the chassis. However, the creation itself of such large scale scrap material is problematic in terms of material costs, and further, there are problems in that costs must be expended on the handling and processing of such scrap material.
Further, a panel type display device such as disclosed in the below mentioned Patent Document 2 also is known. Patent Document 2 discloses a construction for a rectangular frame by assembling together four square-shaped steel tubes. Connection of the square-shaped steel tubes is performed by welding or fixing with screws.    Patent Document 1: Japanese Laid-Open Patent Publication No. 10-255533    Patent Document 2: Japanese Laid-Open Patent Publication No. 2000-92415
Formerly, the fixing structure for optical sheets has been different for each type of display apparatus, and a retaining tool for optical sheets, which can be used in a general or all-purpose manner, has not existed. With such a structure, the costs for the display apparatus cannot be reduced, and further, upon assembling and disassembling the apparatus, the content of the work operations differ for each machine type, and thus are complicated.
Further, in the case of manufacturing the chassis of a large scale flat panel display device as in the prior art, by a sheet metal punching process or a press formation process, there are problems of costs associated with the handling and processing of scrap materials, and thus there have been problems in that manufacturing costs cannot be reduced. Moreover, even with the chassis disclosed in Patent Document 2, in which square-shaped steel tubes are connected, the connecting process cannot be applied to mass production, and thus problems have resulted in that manufacturing costs cannot be reduced.